1. Field of the Invention
This invention relates generally to the simulation of cold temperatures in facilities utilizing a liquid medium such as Freon, liquid nitrogen and helium whose boiling point at one atmosphere provides the controlling temperature. Typical facilities in which this invention could be utilized are thermal vacuum test facilities, optical test facilities, wind tunnel test facilities, coating chambers and other test and manufacturing facilities requiring the simulation of a stable thermal environment.
2. Description of the Prior Art
Thermal simulation has been accomplished in facilities to date by the application of one of the following systems: one, a closed loop, pressurized, forced flow, subcooled system; two, a gravity feed convection system; or three, a boiling mode system. However, there is no thermal simulation system known to the applicants which combines into one common operating system a closed loop, pressurized, forced flow subcooled system together with a gravity feed convection system.
Recently there has been an increasing concern as to the reliability and economic operation of thermal simulation facilities due to the critical nature of the test specimens and increased length of test periods. Thus, there is an urgent need for a thermal simulation system which provides reliability, flexibility and economic operation over a wide range of requirements.
Existing prior art patents which may be pertinent to the present invention are as follows:
U.S. Pat. No. 3,566,960--3/2/71 PA1 U.S. Pat. No. 3,851,274--11/26/74 PA1 U.S. Pat. No. 4,024,903--5/24/77
None of the prior art patents teach the utilization of liquid nitrogen, which, while never completely changing state, is allowed to change slightly into the gaseous form, and thus due to the natural convection thereof, tends to cool the device being tested in the vacuum chamber. U.S. Pat. No. 3,851,274 generally relates to use of liquid nitrogen in a cooling system for a laser device. U.S. Pat. No. 3,566,960 relates to a cooling system for a process that is carried out in a vacuum chamber. U.S. Pat. No. 4,024,903 depicts a cooling system utilizing the natural circulation of cooling water.
None of the known prior art devices offer the new and novel features of the present invention.